MONDAY, Jan. 7 (HealthDay News) -- Most babies who wake up during the night should be allowed to self-soothe and fall back to sleep on their own, researchers say.

"By 6 months of age, most babies sleep through the night, awakening their mothers only about once per week. However, not all children follow this pattern of development," Marsha Weinraub, a Temple University psychology professor, said in a university news release.

"If you measure them while they are sleeping, all babies -- like all adults -- move through a sleep cycle every one-and-a-half to two hours where they wake up and then return to sleep. Some of them do cry and call out when they awaken, and that is called 'not sleeping through the night,' " she added.

In conducting the study, researchers led by Weinraub examined patterns of awakenings during the night among more than 1,200 infants ranging in age from 6 months to 36 months. The researchers asked the babies' parents about their child's awakenings during the night at 6, 15, 24 and 36 months of life. Based on their findings, the researchers divided the babies into two groups: sleepers and transitional sleepers.

By 6 months of age, 66 percent of babies considered "sleepers" did not wake up at night or woke up only once per week, the study revealed.

Meanwhile, at the same age, 33 percent of the children woke up seven nights per week. By the time these babies were 15 months old, they were only waking up two nights per week. At 24 months old, nighttime awakenings dropped to just one night per week, the investigators found.

Most of the babies that woke during the night were boys. These babies -- considered transitional sleepers -- were also assessed as being more irritable or difficult. They were also more likely to be
breast-fed. The mothers of these transitional sleepers were more likely to be depressed and have greater maternal sensitivity, the study authors found.

The authors concluded that genetic factors could play a role in difficult temperaments. "Families who are seeing sleep problems persist past 18 months should seek advice," Weinraub advised.

Babies should learn how to fall asleep without help, the researchers added. "When mothers tune in to these nighttime awakenings and/or if a baby is in the habit of falling asleep during breast-feeding, then he or she may not be learning how to self-soothe, something that is critical for regular sleep," Weinraub said.

More research is needed to explore the link between mothers' depression and infant awakenings, the researchers suggested in the news release.

"Because the mothers in our study described infants with many awakenings per week as creating problems for themselves and other family members, parents might be encouraged to establish more nuanced and carefully targeted routines to help babies with self-soothing and to seek occasional respite," Weinraub noted. "The best advice is to put infants to bed at a regular time every night, allow them to fall asleep on their own and resist the urge to respond right away to awakenings."